/*
 * Copyright (C) 2012 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.reflect;

import com.google.common.annotations.Beta;
import com.google.common.collect.ForwardingMap;
import com.google.common.collect.ImmutableMap;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.Map;

/**
 * A type-to-instance map backed by an {@link ImmutableMap}. See also
 * {@link MutableTypeToInstanceMap}.
 *
 * @author Ben Yu
 * @since 13.0
 */
@Beta
public final class ImmutableTypeToInstanceMap<B> extends ForwardingMap<TypeToken<? extends B>, B>
        implements TypeToInstanceMap<B> {

    /** Returns an empty type to instance map. */
    public static <B> ImmutableTypeToInstanceMap<B> of() {
        return new ImmutableTypeToInstanceMap<B>(ImmutableMap.<TypeToken<? extends B>, B>of());
    }

    /** Returns a new builder. */
    public static <B> Builder<B> builder() {
        return new Builder<B>();
    }

    /**
     * A builder for creating immutable type-to-instance maps. Example:
     * 
     * <pre>
     * {
     *     &#64;code
     *
     *     static final ImmutableTypeToInstanceMap<Handler<?>> HANDLERS = ImmutableTypeToInstanceMap
     *             .<Handler<?>>builder().put(new TypeToken<Handler<Foo>>() {}, new FooHandler())
     *             .put(new TypeToken<Handler<Bar>>() {}, new SubBarHandler()).build();
     * }
     * </pre>
     *
     * <p>
     * After invoking {@link #build()} it is still possible to add more entries and build again.
     * Thus each map generated by this builder will be a superset of any map generated before it.
     *
     * @since 13.0
     */
    @Beta
    public static final class Builder<B> {
        private final ImmutableMap.Builder<TypeToken<? extends B>, B> mapBuilder = ImmutableMap.builder();

        private Builder() {}

        /**
         * Associates {@code key} with {@code value} in the built map. Duplicate keys are not
         * allowed, and will cause {@link #build} to fail.
         */
        @CanIgnoreReturnValue
        public <T extends B> Builder<B> put(Class<T> key, T value) {
            mapBuilder.put(TypeToken.of(key), value);
            return this;
        }

        /**
         * Associates {@code key} with {@code value} in the built map. Duplicate keys are not
         * allowed, and will cause {@link #build} to fail.
         */
        @CanIgnoreReturnValue
        public <T extends B> Builder<B> put(TypeToken<T> key, T value) {
            mapBuilder.put(key.rejectTypeVariables(), value);
            return this;
        }

        /**
         * Returns a new immutable type-to-instance map containing the entries provided to this
         * builder.
         *
         * @throws IllegalArgumentException if duplicate keys were added
         */
        public ImmutableTypeToInstanceMap<B> build() {
            return new ImmutableTypeToInstanceMap<B>(mapBuilder.build());
        }
    }

    private final ImmutableMap<TypeToken<? extends B>, B> delegate;

    private ImmutableTypeToInstanceMap(ImmutableMap<TypeToken<? extends B>, B> delegate) {
        this.delegate = delegate;
    }

    @Override
    public <T extends B> T getInstance(TypeToken<T> type) {
        return trustedGet(type.rejectTypeVariables());
    }

    /**
     * Guaranteed to throw an exception and leave the map unmodified.
     *
     * @deprecated unsupported operation
     * @throws UnsupportedOperationException always
     */
    @CanIgnoreReturnValue
    @Deprecated
    @Override
    public <T extends B> T putInstance(TypeToken<T> type, T value) {
        throw new UnsupportedOperationException();
    }

    @Override
    public <T extends B> T getInstance(Class<T> type) {
        return trustedGet(TypeToken.of(type));
    }

    /**
     * Guaranteed to throw an exception and leave the map unmodified.
     *
     * @deprecated unsupported operation
     * @throws UnsupportedOperationException always
     */
    @CanIgnoreReturnValue
    @Deprecated
    @Override
    public <T extends B> T putInstance(Class<T> type, T value) {
        throw new UnsupportedOperationException();
    }

    /**
     * Guaranteed to throw an exception and leave the map unmodified.
     *
     * @deprecated unsupported operation
     * @throws UnsupportedOperationException always
     */
    @CanIgnoreReturnValue
    @Deprecated
    @Override
    public B put(TypeToken<? extends B> key, B value) {
        throw new UnsupportedOperationException();
    }

    /**
     * Guaranteed to throw an exception and leave the map unmodified.
     *
     * @deprecated unsupported operation
     * @throws UnsupportedOperationException always
     */
    @Deprecated
    @Override
    public void putAll(Map<? extends TypeToken<? extends B>, ? extends B> map) {
        throw new UnsupportedOperationException();
    }

    @Override
    protected Map<TypeToken<? extends B>, B> delegate() {
        return delegate;
    }

    @SuppressWarnings("unchecked") // value could not get in if not a T
    private <T extends B> T trustedGet(TypeToken<T> type) {
        return (T) delegate.get(type);
    }
}
